Patent Literature 1 discloses the method of making a p-type gallium nitride compound semiconductor by use of activation annealing, and a gallium nitride compound semiconductor doped with a p-type dopant is annealed in nitrogen atmosphere.
Patent Literature 2 discloses the method of growing a low-resistance p-type gallium nitride compound semiconductor by vapor phase deposition. In this method, after the p-type gallium nitride semiconductor is grown, the substrate temperature is decreased to 700° C. in an atmosphere composed of ammonia and hydrogen and then decreased from 700° C. in an atmosphere composed of an organic nitrogen compound and nitrogen. Tertiary butylamine, ethyl azide, and dimethylhydrazine are used as organic nitrogen compounds.
Patent Literature 3 discloses the method of making a nitride compound semiconductor. In this method, after a stack structure including a p-type gallium nitride semiconductor layer containing an acceptor is grown, the stacked structure is cooled in an atmosphere composed of a nitrogen source which releases no dissociated hydrogen. The nitrogen sources include amine compounds, hydrazine compounds and azide compounds, such as trimethylamine, dimethylamine, triethylamine, diethylamine, phenylmethylamine, and trimethylhydrazine.
Patent Literature 4 discloses the method of forming a p-type gallium nitride semiconductor. In the period to decrease the temperature of a p-type gallium nitride semiconductor, an atmosphere containing hydride gas is changed to an atmosphere containing hydrogen or nitrogen at a temperature equal to or higher than 400° C. Ammonia is used as the hydride gas.